Metabolomic profiling of blood from Nellore and Angus cattle under heat stress.

Heat stress (HS) negatively affects cattle welfare, productivity, and sustainability, with marked differences between heat-tolerant breeds such as Nellore and heat-susceptible breeds such as Angus. In this study, an untargeted UHPLC-Orbitrap-MS metabolomic approach was used to investigate breed-specific differences in the blood metabolome associated with HS. Blood samples were collected from the same Nellore and Angus steers during peak HS exposure and after recovery, allowing both inter-breed and within-animal longitudinal comparisons. Multivariate analyses revealed a clear metabolic divergence between breeds during the challenge period, involving metabolites related to amino acid metabolism, lipid remodeling, energy pathways, and steroid metabolism. Longitudinal analyses accounting for repeated measures showed pronounced breed-specific metabolic responses. Nellore cattle displayed extensive and statistically robust metabolic changes across phases, with 114 metabolites remaining significant after false discovery rate (FDR) correction, including amino acids and peptides, nucleotide derivatives, carbohydrates, acyl-carnitines, steroids, and tetrapyrrole-related compounds. In contrast, Angus cattle showed only a limited number of FDR-significant metabolites, indicating a less consistent systemic response to HS. Pathway analysis identified porphyrin, purine, and pyrimidine metabolism as key pathways modulated by HS, particularly in Nellore cattle. Overall, these results suggest that heat tolerance is associated with coordinated metabolic adaptations rather than isolated metabolite changes. Further studies on larger cohorts are needed to validate the functional relevance of these findings.